API Review: add `UNBOND` in `EXTRA_REASON` name

> Can you make EXTRA_REASON an 'unsupported app usage' alias for
> EXTRA_UNBOUND_REASON (which is in the public API)?
> And add a max target SDK to the @UnsupportedAppUsage annotation.

Bug: 221851154
Test: Build + TH
Tag: #refactor
Change-Id: I684e56572d1882d02f6f782fa10f3db793fe182d